General interior materials of a vehicle include a door trim, a filler, a trunk mat, a package trim, a headliner, etc. Interior materials of some vehicles are formed to improve their appearances or textures by attaching a soft skin material having an embossed pattern onto a hard base material. That is, some vehicles use interior materials formed by injection-molding only a hard base material while some other vehicles, e.g., high-level vehicles, use interior materials formed by attaching a soft skin material such as fabric onto a hard base material.
For example, polypropylene (PP), PP felt, PP board, acrylonitrile butadiene styrene (ABS), wood stock, or resin felt is commonly used as a hard base material, and felt, fabric, polyvinyl chloride (PVC), or thermoplastic polyolefin (TPO) on which polyethylene (PE) foam, PP form, or polyurethane (PU) foam is bonded is commonly used as a soft skin material to be attached on the base material.
In a typical molding method of an interior material of a vehicle, a skin material having an embossed pattern is inserted into a mold and then a base material (thermoplastic resin such as PP) is injection-molded on a rear surface of the skin material. However, the skin material may be expanded in the mold or the embossed pattern of the skin material may be damaged due to high injection temperature and pressure to cause deterioration in appearance. In order to prevent these problems, Korean Patent Publication No. 10-2008-0033598 discloses a technology of forming an upper mold as a vacuum mold, preheating and then vacuum-sucking fabric onto a bottom surface of the upper mold, and thus preventing damage of the fabric when upper and lower molds are combined, and a technology of previously forming an embossed pattern on the bottom surface of the upper mold, printing the embossed pattern on the fabric in a molding process, and thus improving the appearance of the fabric without damaging the embossed pattern.
However, the above technologies may be easily used in a vertical molding apparatus for vertically moving a skin material and an injected base material, but may not be easily used in a horizontal molding apparatus for horizontally moving a skin material and an injected base material.
In general, an upper mold has to be a vacuum mold for vacuum-sucking fabric and a space between the fabric and a bottom surface of the upper mold has to be sealed to prevent air leakage. As such, basically, the fabric has not to be air permeable and thus is generally formed in a double structure including a skin layer formed of TPO or PVC having a thickness of 0.5 to 1 mm and excellent elongation, and a PP foam layer having a thickness of 2 to 3 mm and excellent thermal resistance, or in a single structure including only a skin layer.
In order to appropriately perform vacuum-suction, fabric is preheated to a temperature equal to or greater than 300° C. before being inserted into a mold. If the preheated fabric is inserted into the mold, the fabric is not flat but is expanded to sag downward. In a typical vertical molding apparatus, fabric that sags downward is horizontally inserted into a mold and thus no problem occurs in a molding process.
However, in a horizontal molding apparatus, since fabric that is preheated and expanded is vertically inserted, the fabric may sag downward due to its weight and thus may be folded. In particular, if the fabric includes only a skin layer to have a small thickness, the fabric may be folded more seriously.
Furthermore, although fabric has to be preheated and then be inserted into a mold as soon as possible, unlike a vertical molding apparatus that may manually insert the fabric, a horizontal molding apparatus has to automatically insert the fabric and thus requires more time in comparison to the vertical molding apparatus.
Due to the above-described problems, only vertical molding apparatuses are developed and horizontal molding apparatuses hardly exist to form an interior material of a vehicle by integrally molding a skin material and a base material.